CROWNVETCH
Coronilla varia L., family LeguminosaePlant:
Crownvetch is a spreading, long-lived, winter-hardy, drought- tolerant, herbaceous legume with angular stems that grow to a height of 2 to 3 feet during the blooming period, after which the plant forms a dense mat about a foot deep. It will grow at fertility levels so low that few other plants will normally survive. Its principal use is for erosion control, soil building, and ground cover (Hawk 1955, Musser et al. 1954, Richardson and Diseker 1963, and Richardson et al. 1963). It is especially valuable for holding banks along highways. The stand improves with age and gradually chokes out other weeds. It is also used for its ornamental value on steep banks and hillsides (Grau 1962). The plant can be established from seeds or crowns (Wheeler and Hill 1957*).
Inflorescence:
Crownvetch produces attractive rose, white, or pinkish-white flowers from June to September. The inflorescence is a contracted raceme, and its flowers are a source of both nectar and pollen, which bees gather. The nectar is not secreted in the usual place but on the outside of the fleshy calyx, where it is sought out by bees (Muller 1883*). They alight upon the petals in the normal manner and probe with their proboscis between the bases of the petals to the outside of the flower for the nectar on the calyx (Knuth 1908*, p. 313, and Muller 1883*). Anderson (1958) stated that the honey bee has to learn how to trip crownvetch blossoms to obtain pollen, the primary attractiveness of the flowers, and, incidentally, to pollinate the blossoms.
The bee straddles the lower section of the flower with its head facing the center of the blossom; then with its two rear legs, the bee pushes the two sides of the blossom outward. This pressure causes the cup of the flower to shorten and the anthers and stigma to snap out where the pollen is available to the bee, and the stigma is exposed to pollination. Anderson also stated (personal correspondence, 1970) that bees have been known to starve on large acreages of crownvetch located in wooded areas of Pennsylvania.
Coronilla, meaning "little crown," is derived from the 202 characteristic crownlike shape of the cluster of blossoms. The specific name, varia, refers to variations in flower color as well as growth habits (Ruffner and Hall 1963).
Pollination Requirements:
Knuth (1908*, p. 313) indicated that crownvetch might not be self- pollinating. However, Todd (1957*) listed it as largely self-pollinated. Grace and Grau (1952) talked of the problem of low seed yields but did not mention pollination. Cope and Rawlings (1970) stated that it is almost completely cross-pollinated, and Al-Tikrity (1969) stated that it is entirely dependent upon insect pollination. Anderson (1958) showed that plants caged to exclude bees produced no seed, while similar plants caged with honey bees produced seed. He stated that a flower head consists of 12 fingerlets with 10 potential seeds in each fingerlet or 120 seeds per head. Eighty seeds per head is considered a good set. In the cage with bees, he obtained only 10 seeds per head, and in the open with few bees present he obtained 18 seeds. He attributed part of the low seed set in the cages to reduced light, but proved that crowavetch is self-sterile and that honey bees can and do pollinate it.
The following year, Anderson (1959) used plastic cages and more bees, and obtained 21.1 seeds per head in the cage and 24.6 seeds per head in the open despite the fact that weather was far less favorable for pollinator activity the second season. He also made repeated counts of pollinating insects in 8- by 50-foot plots, and recorded an average of 14 honey bees and 1.6 bumble bees. Other bees were negligible. Bumble bees visited 2.4 times as many blosoms per minute as did honey bees.
Henson (1963) compared seed production from bagged flowers tripped by hand, rolled, or untouched. The tripped flowers set twice as many seed as the rolled flowers and eight times as many as the untouched flowers. He showed that tripping increased seed production, but even this was low compared to the set obtained by Anderson (1959) when bees were used. Al-Tikrity (1969) reported 150 to 466 lb/acre.
Pollinators:
The observations by Anderson (1958,1959) showed that although crownvetch is not a good source of nectar for honey bees, they are its primary pollinators. Bumble bees visit 2.4 times as many blossoms per minute, but because of the scarcity of these bees they are far less effective and important than honey bees.
Pollination Recommendations and Practices:
Because it requires cross-pollination by insects, and because it is not overly attractive as a nectar source, probably a large number of colonies per acre would be required to provide a heavy bee population within the field. Anderson (1959), with 18 colonies of honey bees on 90 acres of crownvetch, obtained only 14 bees per 400 ft2Ñabout one-third bee per square yard and 24.6 seeds per blossom head (80 seeds per head is considered a good set). This would indicate that many more bees were needed, probably more than one per square yard, or more than one colony for each acre of crownvetch.
Al-Tikrity et al. (1970) suggested that three to four colonies per acre, arranged singly or in groups in rows 200 to 240 yards apart, would provide maximum pollination and result in high seed yields. Later, Al- Tikrity et al. (1972) suggested the moving of honey bees at the start of bloom, then additional colonies as blooming progressed. Sharp (1964) noted that when a good seed crop is being set, the field has a brownish cast. This could be an important factor in judging the effectiveness of the pollinating insects and possible needs for an increase in pollinator population.
LITERATURE CITED:
AL-TIKRITY, W. [S.]
1969. HONEY BEES (APIS MELLIFERA) AS CROWNVETCH (CORONILLA VARIA L.) POLLINATORS. 141 pp. M.S. Thesis, Pa. State Univ. Graduate School.____ BENTON, A. W., CLARKE, W. W., JR., and HILLMANN, R. C.
1970. IMPROVING CROWNVETCH POLLINATION. Amer. Bee Jour. 110: 266 - 267.____ BENTON, A. W., RISIUS, M. L., and CLARKE, W. W., JR.
1972. THE EFFECT OF LENGTH OF STAY OF A HONEYBEE COLONY IN A CROWNVETCH FIELD ON ITS FORAGING BEHAVIOR. Jour. Apic. Res. 11: 51 - 57.ANDERSON, E. J.
1958. POLLINATION OF CROWN VETCH. Gleanings Bee Cult. 86: 281 - 283,318.____ 1959. POLLINATION OF CROWN VETCH. Gleanings Bee Cult.87: 590 - 593.
COPE, W. A., and RAWLINGS, J. O.
1970. INHERITANCE OF FORAGE YIELD AND CERTAIN MORPHOLOGICAL AND FRUITING CHARACTERISTICS OF CROWN VETCH. Crop Sci. 10: 550-553.GRACE, F. V., and GRAU, A. F.
1952. CROWNVETCHÑPROMISING NEW COVER CROP. Crops and SoiIS 4(9): 22-25.GRAU, F. V.
1962. CROWNVETCH ``PENNGIFT', WHAT IT IS, WHAT IT DOES. Gard. Jour. 12(2): 65 - 66,72.HAWK, V. B.
1955. CROWNVETCH, THE KUDZU OF THE NORTH. Iowa Soil DiSt. Watesheds Bul. 3(2): 6,16.HENSON, P. R.
1963. CROWNVETCH - A SOIL CONSERVING LEGUME AND A POTENTIAL PASTURE AND HAY PLANT. U.S. Dept. Agr., Agr. Res. Serv. ARS 34-53, 9 pp.MUSSER, H. B., HOTTENSTEIN, W. L., and STANFORD, J. P.
1954. PENNGIFT CROWNVETCH FOR SLOPE CONTROL ON PENNSYLVANIA HIGHWAYS. Pa. Agr. Expt. Sta. Bul. 576, 21 pp.RICHARDSON, E. C., and DISEKER, E. G.
1963. CROWNVETCH STABILIZES PIEDMONT HIGHWAY BANKS. Crops and Soils 15: 25._____DISEKER, E. G., and HENDRICKSON, B. H.
1963. CROWNVETCH FOR HIGHWAY BANK STABILIZATION IN THE PIEDMONT UPLANDS OF GEORGIA. Agron. Jour. 55: 213.RUFFNER, J. D., and HALL, J.G.
1963. CROWNVETCH IN WEST VIRGINIA. West Va. Agr. Expt. Sta. Bul. 487,19 pp.SHARP. W.C.
1964. CROWNVETCH SEED PRODUCTION. U.S. Dept. Agr. Soil Conserv. Serv., pp. 1 - 5,58-60. Big Flats Plant Materials Center, Big Flats, N.Y.
